textproduct: Rapid City

KEY MESSAGES

- Generally quiet weather in store to start the new year.

- Cooler temps Friday.

DISCUSSION

(This Evening Through Wednesday) Issued at 141 PM MST Wed Dec 31 2025

Latest analysis shows broad upper trough across the eastern CONUS with upper ridging located across the western CONUS, leaving the forecast area in quick moving northwest flow aloft. Deepening 500hpa low located off the southern CA coast with abundant moisture streaming onshore. At the surface, weak low pressure is located in central SD with cold front/baroclinic zone stretching from central MT through northwest SD and into central MT. Low cloud shield on the north side of this boundary is slowly sagging southeast. There is also a wide temperature difference across this boundary, with temps at 18z ranging from the upper single digits in northeast SD to the mid 50s across southwest SD.

There are a couple of tricky aspects to the forecast. The first is the cold front/baroclinic boundary that will wobble southwest/northeast through the forecast period. This will have a dramatic effect on sensible temperatures for those in the vicinity of the boundary. The second minor thing to deal with is the minor ripple in the 500hpa and 700hpa flow that models are showing to pass through the area during the day on Friday. As this system does, it will pull the boundary further south, allowing 850hpa cooler temps to move further west/south into our forecast area, dropping high temperatures when compared to what they will be on Thursday. However, high temperatures will still be above climatic norms for the beginning of January. Additionally, while models also show 700hpa theta-e ridging pushing into the forecast area associated with the 700hpa wave, ensembles show probabilities of receiving any measurable pcpn at less than 10%. Wouldnt be completely surprised to see a flurry or sprinkle fall out of the clouds during the morning hours Friday, but not confident enough to make a mention in the forecast.

For the weekend, upper ridging returns over the Rockies with increasing 500hpa heights and 850hpa temps trending upward. Look for the dry and above seasonal normal temps to continue through the weekend into the first of next week.

AVIATION

(For the 18Z TAFS Through 18Z Thursday) Issued At 1021 AM MST Wed Dec 31 2025

MVFR/IFR conditions in low stratus and fog may develop this afternoon and evening across portions of northwestern SD and persist into the overnight hours. Elsewhere, VFR conditions expected through the TAF period.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.